<?php
interface DB{
function conn();
}

class MysqlDB implements DB{
public function conn(){
echo "mysql conn";
}
}

class OracleDB implements DB{
public function conn(){
echo "oracle conn";
}
}

interface Factory{
function createDB();
}

class MysqlFactory implements Factory{
public function createDB(){
return new MysqlDB();
}
}

class OracleFactory implements Factory{
public function createDB(){
return new OracleDB();
}
}

//调用

$facroty = new MysqlFactory();
$db = $facroty->createDB();
$db->conn();

$facroty = new OracleFactory();
$db = $facroty->createDB();
$db->conn();

实现了对象修改是封闭，对于扩展是开放。

php设计模式（1）-工厂模式